Rhesus monkeys are excellent animal models for biomedical research on aging and a greater use of these primates through cooperative, interdisciplinary approaches has recently been advocated. One aspect of aging research in which rhesus monkeys have been under-utilized is the study of naturally occurring interindividual variation in aging-related changes in behavior ad cognition, neuroendocrine and immune function, or health and disease. The broad aim of this study is to begin a large-scale long-term investigation of the environmental and genetic determinants of interindividual variation in aging-related health and disease processes in the free-ranging rhesus monkey population on Cayo Santiago, PR. The specific aims of this study are to assess the effects of age on several putative somatic, metabolic, and neurobiological aging biomarkers and investigate the extent to which social environmental variables (e.g., dominance rank and social network size) account for interindividual variability in aging biomarkers. Our hypothesis is that the accumulation of allostatic load in low status individuals with little social support might exacerbate aging-related health problems in these individuals. Further, we hypothesize that the neuroendocrine mechanisms underlying the effects of social variables on aging and health may involve long-term changes in the activity of the HPA axis. The study will be conducted in two years. Subjects will be all females older than 15 years of age (n = 56) and a control group with individuals aged between 5 and 15 years. All subjects and controls will be captured once a year for the collection of morphological measures, blood samples, and CSF samples. Plasma cortisol levels measured after capture will be used as markers of stress responsiveness. Plasma cortisol responses to a dexamethasone suppression test will be used to assess glucocorticoid negative feedback. Serum samples will be assayed for blood chemistry variables, and CSF samples for CRH and monoamine metabolites. All subjects will be observed on a weekly basis and fecal samples will be collected and assayed for cortisol and corticosterone. Hormone concentrations will be used as potential predictors of interindividual variation in aging biomarkers along with social variables, age, and genetic relatedness. PUBLIC HEALTH RELEVANCE: This project will provide new information on the relation between environment, aging, and health as well as on the sources of interindividual variability in aging biomarkers in free-ranging rhesus monkeys. These data will enhance our understanding of how nonhuman primates may serve as models for human aging and have implications for the proper clinical diagnoses and care of the elderly as well.